A cartridge is made up of the rim, a case, at least one base wad, and at least one container wad for buckshot. The rim includes the detonating piston and is made of brass or steel, the case contains the gunpowder, the container wad and the buckshot or projectiles. The container wad is a plastic cup-shaped piece that separates the power charge and the buckshot. The base wad fixes the case to the rim through pressure so that they remain joined together both before and after the gunshot. Traditional cartridges comprised a case made of a paper tube provided with a paper base cover and a brass or steel rim together with the explosive powder, an inner wad made of fiber and lead buckshot. With the advent of plastics, the cases and the inner wads were replaced with synthetic plastics derived from petroleum, which were not biodegradable, such as high-density polyethylene.
The wad has a multiple mission: on the one hand, it takes full advantage of the gases produced in the combustion of the powder thanks to a perfect inner sealing of the cartridge at the time of firing, and on the other hand, it contains and protects the buckshot as it makes its way through the interior of the barrel preventing it from deforming due to friction with the walls. Furthermore, thanks to the bending of the joining column of the two cups of the wad, it softens the recoil of the weapon by buffering the initial impact that occurs when firing the weapon.
The use of cartridges made of non-biodegradable plastics presents important ecological problems, as the natural soil is littered with cases and wads or pieces of these without any treatment of the waste. It is in this action of dumping non-biodegradable plastics in nature, without recycling them in any way, wherein environmental contamination occurs, since both the cases and the wads will remain in the soil for centuries before degrading.
Environmental contamination occurs after firing the gunshot when the case is expelled from the weapon and remains on the ground, along with the container wad, since it is projected far way after the gunshot and is also scattered on the ground.
Currently, the most used plastic is high-density polyethylene, which may take ages to disappear from the environment. This is why currently hunting associations and shooting ranges demand a biodegradable cartridge, which also fulfills the proper functions for the development of these sports and activities. Said organic material must meet the technical specifications for use in cartridges, for example, they must have sufficient density and strength for their intended use while the materials that make up the mixture cannot contain any heavy metals or toxic elements.
The degradation of plastic products comprises a first stage involving the disintegration of the material into small particles, and this can be produced by the action of the sun, water, oxidation, microorganisms or heat. Only in the case of authentically compostable materials is a second stage produced within a few months (rather than decades or even centuries, as in the case of other materials) wherein the fragments of the material are converted into volatile materials due to the action of microorganisms, primarily in CO2, water, biomass and energy for microorganisms in the case of aerobic decomposition and in CH4, water, biomass and energy for microorganisms in the case of anaerobic decomposition. Therefore, degradable polymers (only a first degradation phase occurs) should not be confused with bioplastics, which also serve to increase microorganisms, i.e., from which microorganisms obtain energy.
A first response to the demand for biodegradable cartridges has been oxo-degradable plastics, which degrade with the presence of oxygen on a temporary scale that can be determined approximately by the chemical formulation that is added to conventional plastic during the extrusion stage. They are therefore plastics with a controlled lifespan. These plastics need a catalyst that breaks down the long carbon molecules into smaller units in order to facilitate their degradation, instead of relying on bacterial action like bioplastics. Oxo-degradation is a process designed for conventional plastics or non-biodegradable petroleum products. Although it is an improvement over high-density polyethylene, since it is a mixture of a biodegradable polymer and a conventional polymer plus a catalyst, it would only be partially and not totally biodegradable, so that the waste end products are not those established under the EN 13432 standard, and, in the long run, it would continue to deposit non-biodegradable plastics in the environment.
Another alternative to polyethylene and its derivatives has been PVA or Polyvinyl Alcohol, the family of degradable water-soluble plastics. It is soluble in water and absorbs it in large quantities, making it highly problematic in situations of high environmental humidity and it is not suitable for all products, especially for hunting cartridges, where the deformation of the PVA parts directly affects the quality of the cartridge making it very dangerous to use, since humidity is a fixed and inevitable environmental factor that has to be taken into account. Once the absorption of moisture begins, PVA loses it plastic characteristics. An additional problem of PVA is that its use in wetland areas, where it would dissolve in marshes, rivers and lakes would incorporate a synthetic element into the food chain. Furthermore, PVA is toxic in proportions higher than 5%.
Thus ES 2100342 T3 relates to a shotgun cartridge case manufactured by extrusion or equivalent pressure forming a high density polyolefin composition, said composition containing biodegradable starch and a stabilizing compound, the composition being stable in the case until the case is fired, at which time the stabilizing compound is partially destroyed or dispersed so that degradation occurs in the environment in which the case is left. This document relates to a composition containing 43.15% high-density polyethylene and 43% starch, and although the starch is biodegradable, the high-density polyethylene or polyolefin is not, and it also includes cupric stearate, ferric calcium oxide, benzophenone and soya bean oil in its composition. Therefore, it does not meet the biodegradability criteria, since high-density polyethylene, one of its main components, is non-biodegradable. On the other hand, it does not mention the base wad or the container wad that separate the powder from the buckshot and which generates as much or more contamination as the case.
GB 2496180 A describes mortar projectiles in which a vegetable filler is used instead of the usual mineral filler to make it brittle and thus is fragmented at the moment of impact. However, this type of fillers and compositions are not suitable for cartridges, since they are precisely intended to avoid fragmentation. Furthermore, this type of compositions would not withstand the pressures to which the cartridge is subjected, which are greater than those that the mortar projectile has to withstand.
WO 2015/033081 A1 discloses cartridges comprising a mixture of alkyl polysuccinate, polyhydroxyalkanoates (PHA) and vegetable fibers, wherein said PHA is present in proportions of not more than 20% by weight. The fibers make processing difficult and it would be desirable to find biodegradable compositions the mechanical properties of which are more favorable to processing such as, for example, by injection or molding. In addition, the polysuccinate is not biodegradable by itself within a reasonable amount of time, as in the composition described in GB 2496180 A and it requires the action of catalysts and/or the action of light or water to first promote its disintegration. As indicated in WO 2015/033081 A1, degradation is not observed in the absence of light or moisture.
Plastic and rubber cartridges derived from petroleum, such as the current ones, generate a great amount of contamination both in their processing and their degradation. In general, they present great drawbacks that our invention aims to resolve. This invention relates to a clean and odorless biodegradation produced by microorganisms, fungi and algae. None of the foregoing documents describes biodegradable cartridges.